The present invention relates to a method for treating beta-spodumene ceramic articles, and more particularly to a method for treating such ceramic articles with acid in the vapor phase to extract and recover lithium from the ceramics.
The treatment of beta-spodumene ceramics to extract lithium therefrom is well known. Thus, Y. I. Ostroushko et al. disclose, in the Russian Journal Of Inorganic Chemistry, Volume 7, Number 2, pages 126-129 (February, 1962), that lithium can be extracted from mineral beta-spodumene by a hydrogen ion exchange with a strong aqueous acid such as sulfuric acid.
Also known is the fact that a hydrogen-for-lithium ion exchange reaction can proceed in the vapor phase. Thus J. P. Day et al, in "A Study of Chemical Reactivity in Ceramic Heat Exchangers", Transactions of the ASME, Journal of Engineering for Power, Paper No. 78-JT-118, pages 1-5, Gas Turbine Conference, London, England (Apr. 9-13, 1978), describe a test procedure for screening beta-spodumene ceramics wherein exposure of the ceramics to an acid atmosphere in a gradient furnace resulted in an extraction of lithium from the beta-spodumene phase even at sample locations where condensation of the acid from the atmosphere did not occur.
In commercial practice, as shown by U.S. Pat. No. 3,843,981, the treatment of beta-spodumene ceramics to produce lithium free aluminous keatite ceramics involves the leaching of the lithium from the ceramic in a strong acid bath. Modification of these procedures have been developed, for example in U.S. Pat. No. 4,011,091 wherein exposure to the vapors of a refluxing strong acid is also used to modify the properties of the product.
A significant and long-standing problem associated with all of these prior procedures relates to the problem of the reversibility of the lithium ion exchange reaction, i.e., the fact that the presence of significant concentrations of lithium in the leaching medium slows or halts the ion exchange reaction. Thus it has long been the commercial practice to use a large excess of acid over lithium in the leaching solution in order to obtain complete extraction.
This points up a significant economic problem with the commercial process, which is that of reprocessing the volume of spent lithium-containing sulfuric acid leaching medium which is generated by the process. Thus acid which would otherwise be of sufficient strength to continue effective leaching has to be taken out of service because it contains excessive lithium concentrations. And, the commercial value of the lithium and the sulfuric acid present in the spent medium is considerably reduced because of the need for separation processing.
It is therefore a principal object of the present invention to provide a method for treating beta-spodumene ceramic articles which can effectively remove the lithium from the ceramic while avoiding the problems of leachant contamination found in the prior art commercial process.
Other objects and advantages of the invention will become apparent from the following description thereof.